Brain Recording and Stimulation— On the Go!
Post by Anastasia Sares
The takeaway
Researchers have designed a compact, portable device that can record brain activity from patients who already have electrodes implanted in their brain for medical reasons. The expanded capabilities of this device will allow us to test more complex forms of clinical neuromodulation, as well as provide a view into the neuron-level functioning of the human brain in life-like situations.
What's the science?
The number of people with therapeutic electrodes implanted in their brains, though small, is rising. The classic use of this technology is with epilepsy patients, to monitor a region suspected of generating seizures before operating. Nowadays, more permanent devices are being tested which could detect the beginnings of a seizure and deliver a pulse of electricity to stop it in its tracks. Another reason someone might have electrodes implanted is for deep brain stimulation (DBS), which can be used as a treatment for Parkinson’s disease and depression, among other disorders. In addition to their clinical applications, these electrodes are a unique opportunity for researchers to measure human brain activity at the single neuron level.
This week in the journal Nature Neuroscience, Topalovic and colleagues present their new system, Neuro-stack, a wearable device that can connect to a patient’s already-implanted brain electrodes, recording activity and also stimulating particular brain regions.
How did they do it?
The Neuro-stack combines many existing technological elements important to both research and clinical applications, while also increasing their resolution and power. Some features include:
Portability: people can wear the device during an experiment and not be hampered by wires tethering them to computers or other devices.
Simultaneous recording of single-neuron activity and fluctuations of entire neuron populations (known as local field potentials or “LFPs”)
Precise electrical stimulation (sending a pulse of electricity into the brain at a targeted location)
Correction: Statistical techniques to account for electrical stimulations so they don’t interfere with recordings.
Neural networks that can learn what brain activity is relevant for a given task
Eye tracking and a world-view camera, so information from a person’s environment can be synchronized with their brain activity.
What did they find?
The team demonstrated the capabilities of the Neuro-stack in a few small experiments. In one, participants walked around the room while the device recorded activity in the neurons of a region called the hippocampus. Just like in previous experiments with rodents, the hippocampus responded to the person’s location in the room, firing more often when they were close to the walls. This confirms that humans have some of the same navigation mechanisms as rodents when it comes to spatial boundaries.
Another validation experiment was a memory test. In each block, a participant was given a list of ten words to memorize. They then completed a math test as a distracter and finally were asked to recall the words at the end of the block. The authors used a machine learning algorithm (convolutional and recurrent neural networks) to predict which word would be remembered and which would be forgotten based on the activity in the brain at the time of hearing the word.
These experiments were small, proof-of-concept studies and studies with more people would be needed to fully flesh out the findings. However, these small demonstrations show that the Neuro-stack is a useful tool and works as intended.
What's the impact?
Portable implanted electrode systems are often used in animal research and have led to many discoveries about how the brain works. However, a rodent and a human still have many differences, and a rodent cannot converse with a researcher or give feedback about their experiences using language. In addition, certain psychological conditions are difficult to replicate or detect in rodents, limiting clinical research. The Neuro-stack could help to bridge the gap between animal and human research, increasing our understanding of the human brain. Of course, we will have to continue to be vigilant of the ethical implications as our digital and biological worlds collide.
